Re: [time-nuts] how good an oscillator do you need for a GPS simulator
Jim, you're right a DAC is not needed: I was thinking of generating the BPSK by a DAC but it is not necessary. I have seen some BPSK hardware modulators: easier than generating samples and feeding a DAC. On Fri, Dec 16, 2011 at 7:42 PM, Hal Murray hmur...@megapathdsl.net wrote: http://www.ti.com/product/lmk03806 If anybody is collecting a list of common frequencies, there is a table in the data sheet for that chip. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/17/2011 02:37 PM, Azelio Boriani wrote: Jim, you're right a DAC is not needed: I was thinking of generating the BPSK by a DAC but it is not necessary. I have seen some BPSK hardware modulators: easier than generating samples and feeding a DAC. For a single bird a digital output could be made to work, but for a constellation you would need individual bits which would then be mixed together using a resistor network since the birds will not have the same information due to different PN-cods, same rate since they will have different doppler rates etc. etc. Having a three or four bit DAC would be an alternative. Also, the square carrier waves would require more filtering than what a few-bit sine would require. So, saving a DAC is not necesserilly as smart as it looks. Looks like there is room for a GPS/GNSS receiver and simulator list. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
Correct: I was thinking how to simulate an only bird. The RACAL GPS101 is a single channel simulator and maybe made that way. Then it is possible to place a number of 1 channel simulators at a distance... On Sat, Dec 17, 2011 at 3:18 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 12/17/2011 02:37 PM, Azelio Boriani wrote: Jim, you're right a DAC is not needed: I was thinking of generating the BPSK by a DAC but it is not necessary. I have seen some BPSK hardware modulators: easier than generating samples and feeding a DAC. For a single bird a digital output could be made to work, but for a constellation you would need individual bits which would then be mixed together using a resistor network since the birds will not have the same information due to different PN-cods, same rate since they will have different doppler rates etc. etc. Having a three or four bit DAC would be an alternative. Also, the square carrier waves would require more filtering than what a few-bit sine would require. So, saving a DAC is not necesserilly as smart as it looks. Looks like there is room for a GPS/GNSS receiver and simulator list. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/17/11 6:58 AM, Azelio Boriani wrote: Correct: I was thinking how to simulate an only bird. The RACAL GPS101 is a single channel simulator and maybe made that way. Then it is possible to place a number of 1 channel simulators at a distance... I was thinking more along the lines of how would one do a indoor test setup. Magnus's comment was a good one.. if you want to simulate multiple channels, you'd probably want some sort of resistive combiner. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/17/2011 05:10 PM, Jim Lux wrote: On 12/17/11 6:58 AM, Azelio Boriani wrote: Correct: I was thinking how to simulate an only bird. The RACAL GPS101 is a single channel simulator and maybe made that way. Then it is possible to place a number of 1 channel simulators at a distance... I was thinking more along the lines of how would one do a indoor test setup. Magnus's comment was a good one.. if you want to simulate multiple channels, you'd probably want some sort of resistive combiner. Yes, but if you have them all in the same sample clock, adding them together you can do a smaller resistor chain DAC. Three or four bits can be done without much performance setback. Jim, would you be satisfied with L1 C/A only or do you need L1/L2 P-code or even pseudo-P(Y)? Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/17/11 9:01 AM, Magnus Danielson wrote: On 12/17/2011 05:10 PM, Jim Lux wrote: On 12/17/11 6:58 AM, Azelio Boriani wrote: Correct: I was thinking how to simulate an only bird. The RACAL GPS101 is a single channel simulator and maybe made that way. Then it is possible to place a number of 1 channel simulators at a distance... I was thinking more along the lines of how would one do a indoor test setup. Magnus's comment was a good one.. if you want to simulate multiple channels, you'd probably want some sort of resistive combiner. Yes, but if you have them all in the same sample clock, adding them together you can do a smaller resistor chain DAC. Three or four bits can be done without much performance setback. Jim, would you be satisfied with L1 C/A only or do you need L1/L2 P-code or even pseudo-P(Y)? L1 C/A But the real question isn't how to generate the signals (that's straight forward).. it's how good does the oscillator have to be to effectively test the receiver, in the sense of measuring it's timing performance. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/17/2011 11:10 AM, Jim Lux wrote: On 12/17/11 6:58 AM, Azelio Boriani wrote: Correct: I was thinking how to simulate an only bird. The RACAL GPS101 is a single channel simulator and maybe made that way. Then it is possible to place a number of 1 channel simulators at a distance... I was thinking more along the lines of how would one do a indoor test setup. Magnus's comment was a good one.. if you want to simulate multiple channels, you'd probably want some sort of resistive combiner. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/17/2011 09:57 PM, Jim Lux wrote: L1 C/A But the real question isn't how to generate the signals (that's straight forward).. it's how good does the oscillator have to be to effectively test the receiver, in the sense of measuring it's timing performance. A decent OCXO should be able to pull it off. Your receiver should long-term follow your OCXO. Take one of these 40 dollar rubidiums if you are worried. Any drift of a good OCXO will be way within the bandwidth of the GPS channels. This drift would show up as added drift of the GPS oscillator, which is then being tracked and compensated. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/17/11 2:56 PM, Magnus Danielson wrote: On 12/17/2011 09:57 PM, Jim Lux wrote: L1 C/A But the real question isn't how to generate the signals (that's straight forward).. it's how good does the oscillator have to be to effectively test the receiver, in the sense of measuring it's timing performance. A decent OCXO should be able to pull it off. Your receiver should long-term follow your OCXO. Take one of these 40 dollar rubidiums if you are worried. Any drift of a good OCXO will be way within the bandwidth of the GPS channels. This drift would show up as added drift of the GPS oscillator, which is then being tracked and compensated. that is precisely what I was thinking.. I was just wondering if anyone had run across a reason why it wouldn't be the case. (short of actually doing the no doubt tedious analysis) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
Hi Jim, On 12/18/2011 01:25 AM, Jim Lux wrote: On 12/17/11 2:56 PM, Magnus Danielson wrote: On 12/17/2011 09:57 PM, Jim Lux wrote: L1 C/A But the real question isn't how to generate the signals (that's straight forward).. it's how good does the oscillator have to be to effectively test the receiver, in the sense of measuring it's timing performance. A decent OCXO should be able to pull it off. Your receiver should long-term follow your OCXO. Take one of these 40 dollar rubidiums if you are worried. Any drift of a good OCXO will be way within the bandwidth of the GPS channels. This drift would show up as added drift of the GPS oscillator, which is then being tracked and compensated. that is precisely what I was thinking.. I was just wondering if anyone had run across a reason why it wouldn't be the case. (short of actually doing the no doubt tedious analysis) I can offer you several evidence of this: 1) None of the GPS simulators come with very special oscillator, but you may hook up your cesium if you need to for some reason. 2) A typical channel bandwidth typically measures in the Hz range. Tracking drift would not be too hard. 3) While we consider for all practical matter GPS time is stable and the GPS internal reference has incorrect frequency complete with drift, the GPS receiver uses the time-solution of the position to continuously correct the time, frequency and drift of the TCXO (or OCXO). Now, if we move a little of frequency error and drift over to the GPS time of the GPS simulator the receiver won't be able to say as long as the GPS simulator reference isn't drifting like a maniac so that the correction routines can't keep up with it. So, there is my rough analysis for you. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
Hi Magnus: Exactly. The main problem with the Transit system was that the receiver needed a Cs clock for the system to work at all. GPS removed that requirement. It's my understanding that a GPS receiver that uses a Cs clock has much more capability. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/Brooke4Congress.html Magnus Danielson wrote: Hi Jim, On 12/18/2011 01:25 AM, Jim Lux wrote: On 12/17/11 2:56 PM, Magnus Danielson wrote: On 12/17/2011 09:57 PM, Jim Lux wrote: L1 C/A But the real question isn't how to generate the signals (that's straight forward).. it's how good does the oscillator have to be to effectively test the receiver, in the sense of measuring it's timing performance. A decent OCXO should be able to pull it off. Your receiver should long-term follow your OCXO. Take one of these 40 dollar rubidiums if you are worried. Any drift of a good OCXO will be way within the bandwidth of the GPS channels. This drift would show up as added drift of the GPS oscillator, which is then being tracked and compensated. that is precisely what I was thinking.. I was just wondering if anyone had run across a reason why it wouldn't be the case. (short of actually doing the no doubt tedious analysis) I can offer you several evidence of this: 1) None of the GPS simulators come with very special oscillator, but you may hook up your cesium if you need to for some reason. 2) A typical channel bandwidth typically measures in the Hz range. Tracking drift would not be too hard. 3) While we consider for all practical matter GPS time is stable and the GPS internal reference has incorrect frequency complete with drift, the GPS receiver uses the time-solution of the position to continuously correct the time, frequency and drift of the TCXO (or OCXO). Now, if we move a little of frequency error and drift over to the GPS time of the GPS simulator the receiver won't be able to say as long as the GPS simulator reference isn't drifting like a maniac so that the correction routines can't keep up with it. So, there is my rough analysis for you. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
Hi Brooke, On 12/18/2011 03:30 AM, Brooke Clarke wrote: Hi Magnus: Exactly. The main problem with the Transit system was that the receiver needed a Cs clock for the system to work at all. GPS removed that requirement. Indeed. Most of that was due to the long observations times as I recall it. The 4 satellite requirement of a normal navigation GPS receiver is there to allow for a complete (X, Y, Z, T) solution for a portable receiver which can't afford the weight and continuous power consumption of atomic references... at it's time of design. It's my understanding that a GPS receiver that uses a Cs clock has much more capability. The main capability would be to either provide correction/ephemeris data (widely used) or to provide good navigation even under severe methods, as well as direct-Y locking. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
jim...@earthlink.net said: But the real question isn't how to generate the signals (that's straight forward).. it's how good does the oscillator have to be to effectively test the receiver, in the sense of measuring it's timing performance. My 2 cents, which could be way off... One of the things the receiver has to solve for is the actual frequency of the local oscillator. In the process of doing that, the receiver can't tell the difference between an offset in the local crystal and a coordinated offset that's the same in all the transmitter frequencies. So the actual accuracy on a fake transmitter only has to be good enough to fall within the band the receiver thinks is OK. That's a software vs manufacturing/testing issue. If the software will take X ppm but the manufacturing guys are buying crystals good for X/2, the transmitter can be off by X/2. If the software will take X but the manufacturing guys are buying junk crystals, it may not even work with a transmitter that is right on. -- One thing I don't understand about this area. Is the receiver clock offset an independent unknown? The usual reasoning goes that a receiver needs 4 satellites to solve for 4 unknowns: X, Y, Z, and T. If you are willing to assume you are on the surface of the earth, you can get away with only 3 satellites. That's a simple application of N independent unknowns needs N equations. (That's assuming the receiver isn't moving.) Is the receiver frequency another unknown? Do I need another satellite? Or does it drop out somehow? It might drop out. For example, take the 1D case with two satellites. (I know where they are and where they are going.) After I correct for the satellite Doppler, the velocity of the satellites should be zero. I guess that's another equation, so it drops out. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
Maybe they used a Cs standard for the original experimental units, but the first commercial Transit unit I saw (Magnavox MX700?) just had a big OCXO in it - it was also all controlled by a HP2100 computer and output the fix data onto a teletype. The MX1102/1107 (which were pretty much standard equipment on big ships for years) used a rather smaller OCXO, and the MX4102 used a high-grade TCXO. Regards, Pete On Sun, Dec 18, 2011 at 10:30 AM, Brooke Clarke bro...@pacific.net wrote: Hi Magnus: Exactly. The main problem with the Transit system was that the receiver needed a Cs clock for the system to work at all. GPS removed that requirement. It's my understanding that a GPS receiver that uses a Cs clock has much more capability. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/Brooke4Congress.html Magnus Danielson wrote: Hi Jim, On 12/18/2011 01:25 AM, Jim Lux wrote: On 12/17/11 2:56 PM, Magnus Danielson wrote: On 12/17/2011 09:57 PM, Jim Lux wrote: L1 C/A But the real question isn't how to generate the signals (that's straight forward).. it's how good does the oscillator have to be to effectively test the receiver, in the sense of measuring it's timing performance. A decent OCXO should be able to pull it off. Your receiver should long-term follow your OCXO. Take one of these 40 dollar rubidiums if you are worried. Any drift of a good OCXO will be way within the bandwidth of the GPS channels. This drift would show up as added drift of the GPS oscillator, which is then being tracked and compensated. that is precisely what I was thinking.. I was just wondering if anyone had run across a reason why it wouldn't be the case. (short of actually doing the no doubt tedious analysis) I can offer you several evidence of this: 1) None of the GPS simulators come with very special oscillator, but you may hook up your cesium if you need to for some reason. 2) A typical channel bandwidth typically measures in the Hz range. Tracking drift would not be too hard. 3) While we consider for all practical matter GPS time is stable and the GPS internal reference has incorrect frequency complete with drift, the GPS receiver uses the time-solution of the position to continuously correct the time, frequency and drift of the TCXO (or OCXO). Now, if we move a little of frequency error and drift over to the GPS time of the GPS simulator the receiver won't be able to say as long as the GPS simulator reference isn't drifting like a maniac so that the correction routines can't keep up with it. So, there is my rough analysis for you. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/15/11 10:25 PM, Chris Albertson wrote: For testing, I'd assume the gps simulator only needs to be good enough that the receiver will detect the signal. There is some Doppler shift so the receiver must have to look over a wider range of frequencies so if the simulator was inside that range it could work. Light travels at about one foot per nanosecond. so your simulator should need to know the time to within a few tens of nanoseconds. Receivers can deal with not-perfect signal. Multipath and refraction are common. Not just functional test, but to verify the added noise from the receiver. TO just see if it can acquire and track, pretty crummy would work, because it's just like the horrible signals it's seeing off the air You GPS simulator would likely have a GPS receiver inside of it and sync to a real GPS. Not necessarily. You might be testing in a screen room with no external signals available. Clearly, one can go out and spend 500k on a nice Spirent, but I'm looking at what is the few hundred dollar solution. A reasonably quiet oscillator driving an FPGA or playing back bits from RAM On Thu, Dec 15, 2011 at 9:37 PM, Jim Luxjim...@earthlink.net wrote: Say you want a quik n easy n cheap GPS simulator to test a GPS timing receiver. How good does the oscillator (presumably some nice multiple of the chip rate) have to be? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
A used Spirent is only 26K to 37K. Interesting: playing back bits from RAM... can it be that simple? Obvious: a DAC is required. On Fri, Dec 16, 2011 at 3:47 PM, Jim Lux jim...@earthlink.net wrote: On 12/15/11 10:25 PM, Chris Albertson wrote: For testing, I'd assume the gps simulator only needs to be good enough that the receiver will detect the signal. There is some Doppler shift so the receiver must have to look over a wider range of frequencies so if the simulator was inside that range it could work. Light travels at about one foot per nanosecond. so your simulator should need to know the time to within a few tens of nanoseconds. Receivers can deal with not-perfect signal. Multipath and refraction are common. Not just functional test, but to verify the added noise from the receiver. TO just see if it can acquire and track, pretty crummy would work, because it's just like the horrible signals it's seeing off the air You GPS simulator would likely have a GPS receiver inside of it and sync to a real GPS. Not necessarily. You might be testing in a screen room with no external signals available. Clearly, one can go out and spend 500k on a nice Spirent, but I'm looking at what is the few hundred dollar solution. A reasonably quiet oscillator driving an FPGA or playing back bits from RAM On Thu, Dec 15, 2011 at 9:37 PM, Jim Luxjim...@earthlink.net wrote: Say you want a quik n easy n cheap GPS simulator to test a GPS timing receiver. How good does the oscillator (presumably some nice multiple of the chip rate) have to be? __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
On 12/16/11 7:46 AM, Azelio Boriani wrote: A used Spirent is only 26K to 37K. Interesting: playing back bits from RAM... can it be that simple? Obvious: a DAC is required. No.. you don't even need a DAC. The underlying waveform is a binary code that is BPSK modulated. there are a variety of commercial GPS record/playback units that basically are single bit digitizers with no mixer (other than the sampler with a well chosen sample rate to put the GPS signal at a good place in the passband) The GPS receiver we're flying for the CoNNeCT project samples the three bands with a single bit at about 38.6 MHz, which aliases the L1 of 1575 down to about 9 MHz: close to fs/4, which is a convenient place. The other bands alias to convenient places as well. There is some art in picking a good sample rate... you want something that aliases to somewhere convenient, and you want to not have the Doppler push you past a folding point. Doppler from GPS satellite motion to a stationary platform is on order of 5kHz max. For a receiver LEO satellite (probably a worst case) you'd need to add a platform motion of 7 km/s, which is about 10 kHz. Real worst case would be something that's reached escape velocity, which I think is 40-50 kHz Doppler. So don't go picking sample rates that are exact fractions of L1. You'll wind up in alias unwrapping hell. For generating, though, sample rates that are a multiple of the chiprate (1.023 MHz) might be the best strategy. Say you clock the bits out at 10.23 MHz, and you could use the 154th harmonic of the same oscillator as your L1 carrier and all that. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
Slightly peripheral: Just got a bit of TI advertising with a couple of chips of TN interest: http://www.ti.com/product/lmk03806 http://www.ti.com/product/lmk00301 These llok very interesting. 3.3 v i think in cmos mode is enough for most of the instrument external ref inputs. Don Jim Lux On 12/16/11 7:46 AM, Azelio Boriani wrote: A used Spirent is only 26K to 37K. Interesting: playing back bits from RAM... can it be that simple? Obvious: a DAC is required. No.. you don't even need a DAC. The underlying waveform is a binary code that is BPSK modulated. there are a variety of commercial GPS record/playback units that basically are single bit digitizers with no mixer (other than the sampler with a well chosen sample rate to put the GPS signal at a good place in the passband) The GPS receiver we're flying for the CoNNeCT project samples the three bands with a single bit at about 38.6 MHz, which aliases the L1 of 1575 down to about 9 MHz: close to fs/4, which is a convenient place. The other bands alias to convenient places as well. There is some art in picking a good sample rate... you want something that aliases to somewhere convenient, and you want to not have the Doppler push you past a folding point. Doppler from GPS satellite motion to a stationary platform is on order of 5kHz max. For a receiver LEO satellite (probably a worst case) you'd need to add a platform motion of 7 km/s, which is about 10 kHz. Real worst case would be something that's reached escape velocity, which I think is 40-50 kHz Doppler. So don't go picking sample rates that are exact fractions of L1. You'll wind up in alias unwrapping hell. For generating, though, sample rates that are a multiple of the chiprate (1.023 MHz) might be the best strategy. Say you clock the bits out at 10.23 MHz, and you could use the 154th harmonic of the same oscillator as your L1 carrier and all that. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
http://www.ti.com/product/lmk03806 If anybody is collecting a list of common frequencies, there is a table in the data sheet for that chip. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] how good an oscillator do you need for a GPS simulator
Say you want a quik n easy n cheap GPS simulator to test a GPS timing receiver. How good does the oscillator (presumably some nice multiple of the chip rate) have to be? My gut feel is that it needs to be, say, 10x better than the oscillator in the receiver, and you'd compare the timing output of the receiver against a similar timing signal derived right from the simulator's oscillator (e.g. if the timing receiver puts out 1pps, you have your oscillator divided down to 1pps, and you'd compare the two 1ppses) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how good an oscillator do you need for a GPS simulator
For testing, I'd assume the gps simulator only needs to be good enough that the receiver will detect the signal. There is some Doppler shift so the receiver must have to look over a wider range of frequencies so if the simulator was inside that range it could work. Light travels at about one foot per nanosecond. so your simulator should need to know the time to within a few tens of nanoseconds. Receivers can deal with not-perfect signal. Multipath and refraction are common. You GPS simulator would likely have a GPS receiver inside of it and sync to a real GPS. On Thu, Dec 15, 2011 at 9:37 PM, Jim Lux jim...@earthlink.net wrote: Say you want a quik n easy n cheap GPS simulator to test a GPS timing receiver. How good does the oscillator (presumably some nice multiple of the chip rate) have to be? -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
